1. Field of the Invention
The present invention relates to a liquid discharge head substrate and liquid discharge head, and in particular relates to a circuit configuration and liquid discharge head of a liquid discharge head substrate, wherein multiple types of droplet amounts of ink can be discharged in the case of discharging ink with an inkjet method and performing recording onto a recording medium.
2. Description of the Related Art
Liquid discharge heads typically have a heating element (e.g. a heater) at a portion communicating to a discharge port to discharge liquid such as ink provided thereto. An electrical current is applied to the heater to generate heat and boil the ink, thereby discharging ink to perform recording.
However, there has been demand regarding the above-described liquid discharge head regarding improved image quality, higher speed, and lower cost.
In recent years, recording an image with high accuracy by discharging small droplets of ink of under 1 pl has become possible, but with recording only with such small droplets, an image must be formed with a large number of dots, which has the problem of taking a long time for recording. To mitigate such a problem, there is a method wherein large droplets and small droplets are combined within one recording image. In this case a head is configured such that multiple types of liquid droplet amounts of ink can be discharged. Depending on the form, an image may be formed with large droplets only, realizing higher speed, or large droplets and small droplets can be combined to obtain a recording image with high speed and high image quality. Also, by increasing the types of liquid droplet amounts and combining a medium droplet covering between the large droplets and small droplets, a high-resolution image can be obtained with high accuracy and high speed.
Even in fields other than that of recording, there is a demand for discharging large droplets and small droplets. As will be described later, generally a circuit is configured to receive a heat-enable signal for specifying a period to drive each heater and generate heat, so as to be driven for the predetermined period.
As described above, in the case of discharging large droplets and small droplets, in recent years configuration examples have been increasing wherein for example two or more types of heat-enable signals with differing driving time periods (pulse widths) are input to one liquid discharge head. This is so that the energy applied to the heater is changed in accordance with the amount with ink discharge, to discharge two or more types of liquid droplet amounts of ink.
On the other hand, as a method for recording with a greater speed, in recent years there has been a trend toward lengthening the head substrate and increasing the number of heating elements. With such a method, the recording area for each scan of a carriage with a head mounted thereupon is increased, facilitating forming an image at a higher speed. However, such an increasing in heating elements not only increases the size in the substrate lengthwise direction, but also requires additional circuits to drive the additional heating elements, which increases the substrate size in the widthwise direction also. Therefore, the substrate area overall tends to increase greatly.
Generally a semiconductor wafer is employed for an element substrate, so in order to lower the cost of the element substrate, the area of each element substrate needs to be shrunk and the number of element substrates which can be taken from one wafer needs to be increased, but the number of element substrates to be taken from each wafer tends to be decreasing in accordance with increased speeds.
U.S. Published Patent Application No. 2005/0134620 discloses an invention provided to suppress large increases in element substrate area even if the number of heating elements greatly increase. The subject invention has a circuit configuration for each group in increments of a predetermined number of adjoining heating elements. This configuration has an element base unit of the recording head provided for each group which includes an element selection circuit for selecting a common heating element (heater) within each group based on the recording data and a driving selection circuit for selecting one of the recording elements within each group.
An example is disclosed wherein at least one of the element selection circuit and driving selection circuit is disposed adjoined to the driving circuit of each group. That is to say, an example is disclosed wherein a shift register or latch which receives and holds recording data of a number of bits corresponding to the number of groups of time-shared driving is disposed adjacent to a logic circuit for each block.
FIG. 1 illustrates a layout of the element substrate corresponding to the invention disclosed in US Published Patent Application No. 2005/0134620. This configuration includes an ink supply port 101 in the central portion of the substrate and a voltage conversion circuit 107 for generating voltage to drive a driver transistor 103 which is provided at the end portion of the substrate, corresponding to each heater serving as a switching element for whether or not to drive the heater. Also, circuits such as shift registers 106 and latch circuits 105 are disposed along the lengthwise direction of the substrate near the corresponding group of heaters 102 and driver transistors 103.
The shift register 106 is a shift register of 1 bit which synchronizes with the clock signal CLK 109 and serially transfers and stores the recording data. The latch 105 holds the serial data in accordance with the latch signal LT 108. The heaters 102 are divided into M groups of N heaters each. The increments of this group corresponds to the time-shared driving whereby the number of heaters driven simultaneously within one group is one heater. Similarly, the output from the driver transistors 103 and logic circuits 104 also form M groups of N units each.
In addition to the M shift registers as described above, this configuration has n shift registers on the end portion of the substrate, thereby having a total of M+n common shift registers for each heater row. The M+n shift registers 106 and latch circuits 105 are serially connecting.
14 Also, the substrate has a n to N decoder 201 which receives an n-bit time-sharing (block) control signal for driving the multiple heaters with a shifted driving timing in increments of blocks to perform so-called time-sharing driving, and outputs a block selection signal of N bits.
FIG. 2 illustrates a circuit configuration of the inner portion of the logic circuit 104. The recording data (DATA 1 through M) held at the latch circuit is input in a common manner into multiple AND circuits serving as heater selection circuits within each group. The logic circuit takes the recorded data transmitted from the latch 105, the block selection signal from the n to N decoder 201, and the heat-enable (HE) signal for specifying the driving time period (heating time) of the heater as an AND operation with the AND circuit. Selection of the heater for driving and regulation of driving time is then performed. Upon the signal taking this AND operation being boosted with a level converter 205, this is transferred to an arbitrary driver 103, whereby the heater is selectively driven.
Of the M+n shift registers 106 and latches 105, the M first half transfers the data corresponding to the group (1 through M) to the logic circuits 104 within the group. Also, the n latter half of shift registers 106 and latches 105 store and transfer the data for inputting into the n to N decoder 201. The n data (BEDATA 1 through BEDATA n) is converted to a signal for sequentially selecting one of the N heaters within the group by the n to N decoder 201, and is transferred to the logic circuit within each group by the N BLE wirings 204.
By inputting two or more heat-enable signals into one liquid discharge substrate, for example the types of liquid droplet amount of ink can be increased, whereby a recording image with high image quality and high speed can be obtained. However, in accordance with the increasing in number of heat-enable (HE) signals, wiring and circuits for receiving the multiple heat-enable signals and differentiating the use of the heat-enable signals are necessary, whereby the substrate size increases greatly.
With the invention disclosed in US Published Patent Application No. 2005/0134620, the element substrate surface area can be suppressed from increasing greatly even if the number of recording elements increases greatly, thus is a configuration highly effective for higher speed and lower cost, but if this configuration is employed, the element driving circuits are disposed along the array of the recording elements in a long and narrow arrangement. Therefore, if the HE signal increases, not only for the amount of the increased circuits as described above, but the wiring corresponding to the multiple types of HE signals must also be laid, leading to increased substrate size.
FIG. 3 is a logic circuit diagram for one heater row in the case of inputting two types of HE signals into one head substrate. By the number of HE signal types increasing, the HE signal wirings 202 to be laid are increased, whereby the logic circuits 206 wherein the HE signals are input also increase. The HE delay circuits 203 for driving the heater current to be simultaneously driven in each group with a time shift, and reducing noise, also increases.